In humans, the two knee menisci reside between the thigh bone femur and the shin bone tibia. While the ends of the thigh bone and the shin bone have a thin covering of soft hyaline cartilage, the menisci are made of tough fibrocartilage and conform to the surfaces of the bones they rest on. One meniscus rests on the medial tibial plateau; this is the medial meniscus. The other meniscus rests on the lateral tibial plateau; this is the lateral meniscus.
These menisci act to distribute body weight across the knee joint. Without the menisci, the weight of the body would be unevenly applied to the femur and tibia. This uneven weight distribution would cause the development of abnormal excessive forces leading to early damage of the knee joint. The menisci also contribute to the stability of the joint.
The menisci are nourished by small blood vessels but have a large area in the center with no direct blood supply. This presents a problem when there is an injury to the meniscus, as the avascular areas tend not to heal. Without the essential nutrients supplied by blood vessels, healing cannot take place.
The two most common causes of a meniscal tear are traumatic injury and degenerative processes, which are the most common tear seen in all ages of patients. Meniscal tears can occur in all age groups. Traumatic tears are most common in active people aged 10-45. Traumatic tears are usually radial or vertical in the meniscus and more likely to produce a moveable fragment that can catch in the knee and therefore require surgical treatment.
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